MOVEMENTS OF THE INTESTINES 773 



a column of food may remain at the same lev.el in the gut for a considerable 

 time. 



The onward progress of the food is caused by a true peristaltic contrac- 

 tion, i. e. one which involves contraction of the gut above the food mass and 

 relaxation of the gut below. If a balloon be inserted in the lumen of the 

 exposed gut, it will be found that pinching the gut above the balloon causes 

 an immediate relaxation of the muscular wall in the neighbourhood of the 

 balloon. This inhibitory influence of the local stimulus may extend as 

 much as two feet down the intestine towards the ileocsecal valve. On the 

 other hand, pinching the gut half an inch below the situation of the balloon 

 causes a strong continued contraction to occur at the balloon itself (Fig. 355). 



FIG. 355. Intestinal contractions (balloon method). In this dog all the abdominal 

 ganglia had been excised, and both vagi cut. Showing propagated effects of 

 mechanical stimulation above and below the balloon. 



(1) pinch above, (2) pinch below, (3) pinch below balloon. 



Stimulation at any portion of the gut causes contraction above the point of 

 stimulus and relaxation below the point of stimulus (the ' law of the intes- 

 tines '). The same effect is produced by introduction of a bolus of food, 

 especially if it be large or have a direct irritating effect on the wall of the gut 

 (Fig. 356). In this case the contraction above and the inhibition below 

 cause an onward movement of the bolus, which travels slowly down the 

 whole length of the gut until it passes through the ileocsecal opening into 

 the large intestine. The peristaltic contraction involves the co-operation of 

 a nervous system. Whereas in the oesophagus it is the central nervous 

 system which is involved, the peristaltic contractions in the small intestine 

 occur after severance of all connection with the brain and spinal cord. On 

 the other hand, they are absolutely abolished by painting the intestine with 

 nicotine or with cocaine. They must therefore be ascribed to the local 

 nervous system contained in Auerbach's plexus, which we can regard 

 as a lowly organised nervous system! with practically one reaction, 

 namely, that formulated above as the ' law of the intestines.' An anti- 

 peristalsis is never observed in the small intestine. Mall has shown that, 

 if a short length of gut, be cut out and reinserted in the opposite diredion, a 

 species of partial obstruction results, in consequence of the fact that the peri- 

 staltic waves, started above the point of operation, cannot travel downwards 





